The plate thickness and corrugation wavelength of the corrugated steel web (CSW) used in bridge girders are significantly enlarged compared to the corrugated steel plate in buildings, resulting in a higher elastic critical shear buckling stress than the shear yield stress, and hence the failure may occur in an elastoplastic state. This paper investigates the shear failure mechanism of local buckling-dominated large-scale CSWs used in bridge girders. Shear tests of three beams with standard large-scale CSWs and corresponding nonlinear finite element analyses are carried out. The failure mode, typical load–deflection curve, out-of-plane deformation, and strain distribution are obtained. Besides, the effects of initial imperfections on shear behaviors are analyzed in detail. The results indicate that the shear failure of local buckling-dominated large-scale CSW presents elastoplastic buckling of two adjacent sub-panels across the fold interactions, which shows typical characteristics of snap-through instability. The shear loading process can be divided into four stages: elastic stage, elastoplastic stage, buckling stage, and post-buckling stage. The large-scale CSW belongs to a type of imperfection-sensitive member. The initial imperfections make the local sub-panel enters a plastic state before the nominal shear yield load is reached and the shear stress no longer uniformly distributes over the web height. The ultimate shear capacity and initial yield load decrease significantly with the increase of the imperfection amplitude, and the out-of-plane deformation increases with the imperfection amplitude. The elastoplastic shear buckling mechanism of local buckling-dominated large-scale CSWs is explained based on a rigid-bar frame model.